1. Field of the Invention
The present invention relates to a rubbery polymer and a method for producing the same. More particularly, the present invention is concerned with a rubbery polymer comprising a conjugated diene polymer and, bonded thereto, a lithium-detached residue of a lithium-containing organic polymer used as a catalyst (hereinafter, frequently referred to simply as an "organolithium catalyst") in the production of the conjugated diene polymer, wherein the lithium-containing organic polymer is obtained by reacting an organolithium compound with a first polymerizable material comprising at least one conjugated diene monomer and a second polymerizable material comprising at least one aromatic vinyl compound, which second polymerizable material contains at least one multi-vinyl aromatic compound having at least two vinyl groups, and wherein the lithium-containing organic polymer has a specific narrow molecular weight distribution. The present invention is also concerned with a method for producing the above rubbery polymer, which comprises polymerizing at least one conjugated diene monomer in the presence of a specific lithium-containing organic polymer as a catalyst. The rubbery polymer of the present invention is advantageous in that, by using it as a reinforcing agent for a styrene polymer resin, there can be obtained a high impact styrene polymer resin composition which is useful for producing a shaped article having an excellent balance of impact resistance and appearance (luster). Examples of shaped articles which can be produced from this high impact styrene polymer resin composition include housings and other parts for household electric appliances, automobile parts, parts for office equipment, general sundry goods, footgear, toys and various industrial materials. The rubbery polymer of the present invention is also advantageous in that it is useful as an asphalt modifying agent for improving the properties of an asphalt to be used in, for example, road paving, production of a waterproof sheet and roofing.
2. Prior Art
Styrene polymers have not only excellent rigidity, excellent transparency and excellent luster, but also good moldability. Therefore, styrene polymers are widely used in various application fields. However, styrene polymers have a large defect in that it has poor impact resistance. In order to remove this defect, it has been attempted to use various types of unvulcanized rubbers as reinforcing agents for improving the impact resistance of styrene polymers. Thus, various types of rubber-reinforced styrene polymers have been proposed. Among such various rubber-reinforced styrene polymers, commercially widely produced are high impact styrene polymer resin compositions comprising a rubber-modified styrene polymer resin obtained by a method in which at least one vinyl aromatic monomer is subjected to radical polymerization in the presence of an unvulcanized rubbery polymer, to thereby obtain a rubbery polymer having a styrene polymer grafted thereon.
As representative examples of such rubbery polymers usable as a reinforcing agent for improving the impact resistance of styrene polymers, there can be mentioned polybutadiene and a styrene-butadiene copolymer. Of them, polybutadiene is widely used since it can impart especially excellent impact resistance to styrene polymers.
Generally, such polybutadiene and a styrene-butadiene copolymer have been produced by a method in which, as a polymerization catalyst, use is made of an organomonolithium compound, such as n-butyllithium or sec-butyllithium.
However, there have also been reported production methods for rubbery polymers, in which, as a polymerization catalyst, use is made of a reaction product obtained by a process comprising reacting an organomonolithium compound with a multi-vinyl aromatic compound. Examples of such polymerization catalysts used for producing rubbery polymers include a reaction product obtained by reacting an organomonolithium compound with a multi-vinyl aromatic compound (Unexamined Japanese Patent Application Laid-Open Specification No. 48-103690), a reaction product obtained by a method in which an organomonolithium compound is reacted with a conjugated diene compound or a mono-vinyl aromatic compound, and the resultant is reacted with a multi-vinyl aromatic compound (West German Patent No. 2003384), and a reaction product obtained by a method in which an organomonolithium compound, a conjugated diene compound and a multi-vinyl aromatic compound are simultaneously reacted with one another (Examined Japanese Patent Application Publication Nos. 43-25510 and 51-44987). Each of the polymerization catalysts disclosed in the above patent documents has a broad molecular weight distribution. When such a catalyst having a broad molecular weight distribution is used in the production of a rubbery polymer and the obtained rubbery polymer is used in a high impact styrene polymer resin composition, a shaped article obtained using the resin composition is caused to have an unsatisfactory balance of impact strength and appearance.
In recent years, the above-mentioned high impact styrene polymer resin compositions have been used in a wide diversity of application fields, such as housings and other parts for household electric appliances, automobile parts, parts for office equipment, general sundry goods and toys. In accordance with this diversification of the application fields of the high impact styrene polymer resin compositions, these compositions have been required to be increasingly improved with respect to various properties, and it is especially strongly desired that the high impact styrene polymer resin compositions exhibit a good balance of impact resistance and appearance.
Generally, a high impact styrene polymer resin composition is produced by a method in which a rubbery polymer comprising a conjugated diene polymer (such as polybutadiene or a styrene-butadiene copolymer) is dissolved in a styrene monomer, and the resultant mixture is subjected to bulk polymerization or bulk-suspension polymerization while stirring.
In general, the impact resistance of a high impact styrene polymer resin composition, containing a rubbery polymer, can be improved by increasing the rubbery polymer content thereof. However, when the rubbery polymer content of a high impact styrene polymer resin composition is increased, the luster of a shaped article produced from the resin composition becomes poor. The luster of such shaped article can be improved by decreasing either the rubbery polymer content of the resin composition or the particle diameter of the rubbery polymer; however, in either case, the impact resistance of the resin composition becomes markedly low.
Thus, with respect to high impact styrene polymer resin compositions containing a rubbery polymer, there has been a technical dilemma in that impact resistance and luster cannot be simultaneously improved. In other words, there has not been a high impact styrene polymer resin composition having a good balance of impact resistance and luster.
For solving the above problem, various methods have been proposed for producing a high impact styrene polymer resin composition having a good balance of impact resistance and luster. Examples of such proposed methods include a method in which use is made of a rubbery polymer comprising a conjugated diene polymer having a specific solution viscosity (Examined Japanese Patent Application Publication No. 58-4934), a method in which use is made of a rubbery polymer comprising a conjugated diene polymer wherein the solution viscosity and the Mooney viscosity satisfy a specific relationship (Examined Japanese Patent Application Publication No. 53-44188), and a method in which use is made of not only a rubbery polymer comprising a conjugated diene polymer having a specific solution viscosity but also a cross-linked polymer produced using an organic peroxide wherein the tensile modulus and the degree of swelling of the cross-linked product satisfy a specific relationship (Unexamined Japanese Patent Application Laid-Open Specification No. 60-25001). The high impact styrene polymer resin compositions produced by using these methods have an improved balance of impact resistance and luster, as compared to that of a high impact styrene polymer resin composition containing polybutadiene as the rubbery polymer. However, the improvement in the balance of impact resistance and luster, achieved by these methods, is frequently unsatisfactory.
Unexamined Japanese Patent Application Laid-Open Specification Nos. 61-143415, 63-165413, 2-132112 and 2-208312 disclose methods for improving the impact resistance and appearance characteristics of a high impact styrene polymer resin composition, which methods employ, as a rubbery polymer, a styrene-butadiene block copolymer having a specific block configuration. However, it has been found that these methods are unable to provide a practically satisfactory balance of impact resistance and appearance.
As another type of a high impact styrene polymer resin composition, there is known a rubber-modified styrene-acrylonitrile copolymer, that is, the so-called ABS resin. Generally, an ABS resin is produced by a method in which styrene and acrylonitrile are grafted by emulsion polymerization on a polybutadiene rubber latex having a desired particle diameter and a desired cross-linking degree. ABS resins are advantageous in that they are excellent in luster, impact resistance and rigidity. However, an emulsion polymerization, which is used for producing an ABS resin, requires not only cumbersome operations but also a large amount of energy, so that an emulsion polymerization is economically disadvantageous. In addition, since an emulsion polymerization produces waste water, equipment for treating the waste water is required.
Further, it has recently been proposed to produce an ABS resin not by an emulsion polymerization, but by a non-emulsion polymerization selected from a bulk polymerization, a bulk-suspension polymerization and a solution polymerization. Specifically, in this method, a rubbery polymer is dissolved in a mixture of styrene and acrylonitrile and the resultant mixture is subjected to a bulk polymerization, or a bulk-suspension polymerization or a solution polymerization. This method is attracting attention since it has advantages not only in that the content of impurities in the obtained ABS is small and, hence, the ABS is less likely to suffer discoloration, but also in that there is no need for waste water treatment, thus providing an economic advantage over the emulsion polymerization method. However, an ABS resin produced by a non-emulsion polymerization has disadvantages in that not only is the particle diameter of the dispersed rubber particles large, but also the grafting of the styrene and acrylonitrile on the rubbery polymer becomes unsatisfactory, so that the obtained ABS resin has not only poor impact resistance but also poor luster.
In order to solve the above-mentioned problem of the ABS resin produced by the non-emulsion polymerization method, there have been proposed improved non-emulsion polymerization methods for producing an ABS resin. Examples of such improved methods include a method in which use is made of a rubbery polymer having a low solution viscosity (Unexamined Japanese Patent Application Laid-Open Specification Nos. 63-199717 and 63-207803), and a method in which use is made of a rubbery polymer comprising a specific styrene-butadiene block copolymer (Unexamined Japanese Patent Application Laid-Open Specification No. 2-185509). However, these non-emulsion polymerization methods are unable to provide an ABS resin having a satisfactory balance of impact resistance and luster.
As apparent from the foregoing, a satisfactory high impact styrene polymer resin composition having a good balance of impact resistance and luster has not been produced by using a rubbery polymer, such as polybutadiene or a styrene-butadiene copolymer, which is produced by using a conventional anionic polymerization catalyst.
The primary task of the present invention is to solve the above problem of the prior art, that is, to provide an excellent rubbery polymer which can be advantageously used for the production of a high impact styrene polymer resin composition having an excellent balance of impact resistance and luster.